.. ECHINOIDEA. II. 



^4 



specimens of anv Echinothurid hitherto examined (leaving aside the very doubtful Asthenosoma liystrix 

 of 3-I""" figured in Rev. of Ecli., PL II c.) are those of 3'"™ in diameter de.scribed by me (Part I. p. 174). I 

 have stated there that the periproct is, even in the smallest specimens, covered by a number of small 

 irregular plates, with no larger between. So a central plate seems never to be found here.» Since in 

 this very young stage the anal plates are thus already present in considerable number and do not show 

 an}- trace of five original larger plates covering the whole anal area, I do not think we are justified 

 in assuming that these 5 large plates are found in a yet earlier stage. I give here a figure of the anal 

 area of the youngest specimen of Phormoso?)ia (scarceh 3"'") seen by me. (Fig. 1.) 



A matter of much more importance, however, is the statement (p. 91) that in -= Phonnosoma 

 Itispidinii the bare interambulacral area adjoining the primordial plate is covered with a few minute, 

 elongate, irregularlv arranged plates, which correspond to the interradial buccal plates of Cidaris . 

 The same thing is stated for Kamptosovia indistinctiiin (p. ii2|: In this species .... we find a few of 



the same irregular elongate interambulacral plates which in the 

 Cidaridae are as well and as regularlv developed as the ambu- 

 lacral buccal plates . It was hitherto assmned to be one of the 



; , most important features distinguishing the Cidaridw from all 



' V ■ the other regular Echinoids that both the ambulacral and inter- 



ambulacral plates continue over the peristome; the Echiiiothvrida- 

 were distinguished b\- the ambulacral plates alone continuing 

 ■ over the peristome. If these small plates of the peristome found 



' in the two Echinothurids b>- Professor Agassiz were really 



■vM'^"'' homologous to the interradial Ijuccal plates of the Cidarida- this 



fundamental character would have to be given up. Fortunateh', 

 the figures given by Agassiz himself afford the proof that 



Fig. I. Apical sv.stem of a young Phormo- , , , , ■ ^^ ^-i ■ ^ j- , i i 



" f, / . ,.• ,° „, these plates are not homologous with the niterradial buccal 



soma placenta, 3'""i in aiameter. ^b'j. r o 



plates of the Cidarids; since the primordial interambulacral 

 plate is persistent, these small plates lying in the buccal membrane inside (adorally) the primordial 

 plate cannot possibly have any relation whatever to the interambulacral plates and cannot be said to 

 -correspond to the interradial buccal plates of Cidaris . The\ correspond to those small, irregular 

 plates found in the peristome of the other regular Echini. 



In treating the Echinothurids in Part I, I had to lea\e ii/crrftr srdis the si)ecies iPhormosoma 

 panamensc and hispiduvi. and Profes.sor Agassiz, not recognizing my limitation of the genus IVior- 

 mosoma. does not take the trouble to state to which group tlie.se s])ecies belong. Rut from the very 

 careful description and figures of the test combined with iii\ ix;uninali<m of the pedicellarite of the 

 type specimens in the U. S. National Museum, it can be said with certainl\ that they belong to the 

 genus Echinosomn. It is true that the character of the primary actinal spines of puiKuiniisc is unkmnvn, 

 but all the other characters are decidedly those of Eclihiosoiiid. so that I think we may safely conclude 

 that the spines also are tipped with a hoof and not provided with a fleslu sack. A more detailed de- 

 .scription of the pedicellaria: I cannot give on this occasion; it will suffice to say that they agree rather 

 closely with those of Echinosoma uranus and tenue\ in panavicnsc I have not, however, found the 



